Correct me if I'm wrong but an SLR will have a mirror. These aren't SLR's right?

They made (I know of a canon one anyway) that the mirror didn't move, it was transparent and the film was basically looking through the mirror. Just one less moving part and the camera was very quiet. The problem with that was that any crap on the mirror was now seen on the film.

The camera's you are talking about, how does the eye piece work? Is it just like a video camera, you're looking a screen rather than actually looking thru the lens?

You are looking at the screen. Some have an electronic viewfinder as an accessory. Some, like the Sony NEX7 are really nice cameras. Sony is releasing a full sensor one shortly here. The rest are APS-C sized sensors.

Nice summary Trunk, will be helpful for sure. I picked up a GX1 a few months ago to experiment with and have been pretty pleased with it and the Panasonic 14mm pancake lens. Very lightweight compared to the Canon 30D/10-22mm I was using on occasion. Not quite the same quality, but good enough. I really like the 4:3 aspect ratio, but that's personal preference. A few observations in the dozen or so dives I've done with it...

1. The remote shutter needs an adapter to work with standard switches, but not very difficult to make. I built one from a connector I bought at Radio Shack, a couple of resistors, and a 2.5mm right angle plug I ordered online.

2. The Custom modes on the dial is nice, it can be programmed with most camera settings you need for skydiving, such as manual mode settings, disable touch screen, JPG format, etc. Except for the manual focus point, that needs to be set every time you let the camera auto-focus. Pretty easy though, especially with the zoom feature, and it will remain in place after power off. All the lenses (that I have) are electronically focused, so moving the zoom ring with the power off doesn't affect it. There's no reason the manual focus point could not be part of the custom settings, but not something they figured people would use I guess.

3. FPS is a bit low, but perfectly fine for me. With my SD card (class 10 Sandisk Extreme) I get about 5 seconds at full rate, then about 2 fps after. I clears the buffer pretty fast though, so it's nearly always ready for full-burst shooting. I should note it does have a 20fps shutterless burst mode, but quality is poor. I would be tempted to try the Olympus PEN models if you need a faster fps.

4. It has an auto-ISO feature in all modes EXCEPT in manual mode. Which sucks, because it'd be nice to lock the shutter and aperture and have it auto-ISO the exposure. As it is now, I guess at a decent ISO depending on light conditions so that my aperture remains high enough for a decent DOF. I hear the Olympus PEN models have this feature though. Since it's just a firmware issue, I contacted Panasonic and actually got a reply saying they forwarded it to their R&D department, who knows...

5. Good ISO performance, at least as good as my 30D I'd wager, even though it's a smaller sensor (2x crop factor instead of 1.6x). I have no issues using 1600 or 3200 if need be.

6. Did I mention it's small and light? I don't even notice it on my head until I smack it on the ceiling or door of the plane. D'oh!

7. The SD card slot is on the bottom of the camera, so removing the card is a pain. Not really an issue for me, but a working stiff might be a bit frustrated.

Overall I'm pretty pleased with the results. It's not quite in the same league as my 30D, but the more I've used it the more content I am with the new format. The smaller size is priceless, though it's not really much cheaper than a standard Canon Rebel setup.

I was a bit bummed at there being no inexpensive options for super-wide angle, but you can pick up the excellent Panasonic 14mm from Ebay for a good price and slap a Panasonic DMW-GWC1 wide-angle converter on it to get to 12mm (24mm equivalent) without adding much extra weight. The attached pic was with the wide-angle attached. ISO160, 1/640s @ f5.6.

Trunk, Thanks for putting that together. I currently own the Panasonic GX1, Sony Nex 5N, and the Olypmus E-PM1 and have used the Olympus and Panasonic For skydiving and wanted to add my thoughts:

Panasonic (with 14mm Pancake lens) - My current favorite of the ones i've tried it has the best remote connection and controls and the pictures turn out well. Pros: Good external controls - as well as menus within the camera. Best remote connection. Cons: Heaviest of them all(but still lighter than a DSLR). Battery and card door are on the bottom - if you are using this for work and have to give an editor your SD card this could be an issue. Really right stuff makes a nice plate for this camera that allows access.

Get Hypoxic just started offering a remote adapter, or you can put one together with a 2.5 mm to 2.5 mm Female adapter from radio shack and a cord off of a cheap remote you can find on amazon - no splicing or cutting of wires involved just plug and play(I have the link if anyone needs it).

Olympus(with 14mm pancake lens): Pros: Good photos, Fast FPS Cons: User interface isn't that great, can't use the remote with some settings. Remote connection is not very good - I had to stop using mine because the connector kept coming out in freefall. Card/Battery door on bottom.

Used the same thing to make a switch adapter 2.5 to 2.5 mm female from radio shack and a remote cord from a camera switch for olympus(no cutting or splicing just plug and play).

Sony NEX 5N (haven't used this in freefall yet) Pros: Best photos of the bunch(but not by much), Fast FPS, Lightweight (olympus is lighter). Best video options (1080p at 60fps) . Cons: In menu camera system (I like external controls). Have to have the camera switch installed (i'm not willing to do that). Lenses are heavy - not as a good a selection yet as the M43 system either. Card/Battery door on bottom.

Overall Recommendations: Panasonic if you want a camera that has a no hassle remote option and takes good pictures.

Olympus if you are going for the lightest possible setup - Tape the connector in and never take it out (or find someone to make a right angle connector)

Sony: Only if you are a fan of sony's and this camera and don't mind spending the time or the money to modify it (I am not). I plan to use it for high quality video in freefall when I need a step up from my CX110 or go pro. (Google Sony NEX 5n video and see what some people are doing with this camera for normal cinematography)

Correct me if I'm wrong but an SLR will have a mirror. These aren't SLR's right?

They made (I know of a canon one anyway) that the mirror didn't move, it was transparent and the film was basically looking through the mirror. Just one less moving part and the camera was very quiet. The problem with that was that any crap on the mirror was now seen on the film.

The camera's you are talking about, how does the eye piece work? Is it just like a video camera, you're looking a screen rather than actually looking thru the lens?

EOS RT - I had one. It was fantastic for sports photography at the time.

SLR strictly means single lens reflex - the "reflex" part meaning that by definition it should have a mirror. It seems to be evolving however into a definition for any camera where you see the same image through the viewfinder as the sensor is getting. Once that becomes as good as real time, then its fine with me.